Even if you live in a big city, there are probably tons of open spaces to explore in your backyard. But you don't even know it. If you're an avid hiker, or even if you dabble, Sierra Club Trail Explorer for iPhone is a wonderful guide to the great outdoors.

What does it do?

Powered by AllTrails.com, it lets you browse and search more than 40,000 trails in North America. It's chock-full of resources, listing a description of the path, and showing maps, activities, level of difficulty, and photos.

Why do we like it?

Sometimes, if you head out on a trek, you'll arrive at the trailhead, look at the yellowing, weather-damaged map, and hope you won't get lost. But this app works as your guide, with all the information you need. And with offline access, you don't even need an Internet connection. Plus, it's interactive. You can make a wish list of places you'd like to visit, and check in when you arrive. Additionally, you mark your favorites, in case you ever want to revisit a spot you liked, and add your own reviews and pictures. If you're planning some kind of walkabout, or even a day trip, you'll want to download this app.